This invention relates to an infrared projector for projecting infrared radiation analogous to two-dimensional infrared spectral luminance distribution information about an infrared scene, etc., produced by a computer, etc, based on the luminance distribution information. For example, the infrared projector is used in the evaluation of infrared equipment in such a way that an infrared image can be obtained by imaging infrared radiation projected by the projector using an infrared imaging device, that the infrared spectral luminance data and the infrared image are compared, and that the imaging capability of the infrared imaging device is evaluated by the degree of degradation of the infrared image.
FIG. 5 is a conventional infrared projector shown in George C. Goldsmith, xe2x80x9cCharacterization measurement of the wideband infrared scene projector resistor arrayxe2x80x9d, SPIE, Vol. 2742, P25-37(1996). A fine heating element array 1, a controller 2 for the fine heating element array 1, and a projecting reflector 3 for projecting infrared radiation radiated from the fine heating element array 1 are shown.
Next, the operation is described. As fine heating elements are arranged as a two-dimensional array in the fine heating element array 1, a two-dimensional infrared spectral luminance distribution can be produced by making the heating value of each heating element different from that of the others. Each heating element is composed of a resistor, and the amount of infrared radiation can be adjusted by changing the voltage applied to the resistor.
The controller 2 receives the two-dimensional infrared spectral luminance distribution information of an infrared scene, etc., produced by a computer, etc., converts the spectral luminance distribution into a voltage distribution which is applied to each heating element, and controls the voltage to be applied to each heating element. When constructed in this way, the infrared radiation radiated from the fine heating element array 1 is imaged by using the infrared imaging device and then an infrared image can be obtained.
FIG. 6 shows a part of the fine heating element array 1. A resistor 4 in FIG. 6 is connected to the controller 2 through a lead wire 5. When a voltage is applied to the resistor 4 from the controller 2, current flows through the resistor 4 and heat is generated. The relation between the voltage V and the amount of heat generation P in the resistor 4 having a resistance R is expressed by P=V2/R.
As infrared radiation is radiated from the resistor 4 in proportion to the heat generated, the amount of infrared radiation radiated by the resistor 4 can be controlled by controlling the voltage applied to the resistor 4 by the controller 2.
As thermal diffusion takes place when air exists around the fine heating element array 1, the radiation efficiency of infrared radiation to be radiated from the fine heating element array 1 is reduced. Therefore, the fine heating element array 1 is placed in a vacuum package (not illustrated in particular). Moreover, the infrared radiation to be radiated from the fine heating element array 1 is transmitted out of the package through a ZnSe window having good transmittance characteristics over a wide frequency band.
Furthermore, in order to improve the temporal response when the fine heating element array 1 changes from a high temperature to a low temperature, the heat is dissipated through a lead wire 5. When the amount of the heat dissipation is increased too much, however, the fine heating element does not achieve the desired temperature. Thus, the amount of heat dissipation and the ability to improve the temporal response time is limited. In other words, the temporal response in temperature change from a high temperature to a low temperature is quite unfavorable in this projector.
Next, the characteristics of infrared radiation radiated from the fine heating element array 1 are described. FIG. 7 shows the wavelength characteristic of the amount of infrared radiation in the infrared projector, where the horizontal axis represents wavelength and the vertical axis represents the intensity of the infrared radiation. The characteristic of the fine heating element array 1 is indicated by M in FIG. 7, and the characteristic of infrared radiation radiated by a black-body at the same temperature as that of the fine heating element array 1 is indicated by 762 K. The maximum temperature at which projection can be made using the projector is 762 K, and projection at temperatures higher than this cannot be made otherwise serious errors will occur.
Furthermore, the reason why the amount of infrared radiation of the fine heating element array 1 is lower when compared to that of a black-body light source is that the degree of integration of the heating elements is low and the infrared emissivity of the heating elements themselves is low (it is estimated to be 0.6 in the paper concerned). In this way, when the amount of infrared radiation is low, the infrared projector has lower contrast and becomes difficult to use.
In the conventional infrared projector constructed as in the above,
a) it was required to newly develop a fine heating element array for specialized use in an infrared projector, and the heating element array was expensive,
b) because the temporal response to temperature changes is poor since heating elements are used, and because a spacing is required between elements in the array as the heating elements need lead wires, and further because of some other reasons, the temporal resolution and spatial resolution were poor,
c) because the temperature of the fine heating element is limited, the simulation of a high-temperature body could not be performed,
d) the intensity distribution of infrared radiation generated by the fine heating element array had poor contrast, the accuracy of the simulation was poor, and some other problems existed.
The present invention was made in order to solve the problems described above, and it is an object of the present invention to provide an infrared projector in which it is not necessary to develop arrayed elements radiating infrared radiation, a high temporal resolution and a high spatial resolution are obtained, the simulation of a high temperature body is obtained, the wavelength and luminance characteristics are controlled, a high contrast and a high simulation accuracy are made available, and so on.
Considering the above-mentioned objects, an infrared projector of the present invention comprises a micromirror device as an optical modulator for changing the direction of reflection by providing a plurality of mirrors and changing the direction of each of the plurality of mirrors independently, a controller for controlling the direction of each mirror of the micromirror device, and an infrared light source for irradiating the micromirror device with infrared light.
Furthermore, in the present invention, a high-temperature black-body furnace is provided as the infrared light source.
Furthermore, in the present invention, an infrared wavelength selection means for selecting the wavelength of infrared radiation incident on the micromirror device is provided.
Furthermore, in the present invention, two or more bandpass filters having different passbands are provided as the infrared wavelength selection means.
Furthermore, in the present invention, a diffraction grating is provided as the infrared wavelength selection means.
Furthermore, in the present invention, movable supporting means for tilting the diffraction grating with respect to incident direction of infrared radiation is provided as the infrared wavelength selection means.
Furthermore, in the present invention, two or more diffraction gratings having different grating pitches are provided as the infrared wavelength selection means.
Furthermore, in the present invention, a prism is provided as the infrared wavelength selection means.
Furthermore, in the present invention, a movable supporting means for tilting the prism with respect to the incident direction of infrared radiation is provided as the infrared wavelength selection means.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.